A transmission refers particularly to a multi-ratio transmission in which a multiplicity of gear ratios, that is to say transmission ratios, between the drive shaft and the output shaft are selectable, preferably in automatic fashion, by shift elements. The shift elements are in this case for example clutches or brakes. Such transmissions are used particularly in motor vehicles for the purposes of suitably adapting the rotational speed and torque output characteristics of the drive unit to the driving resistances of the vehicle.
An automatic transmission for a vehicle is known from the publication DE 102 13 820 A1. However, said automatic transmission does not have an electric machine.
In the prior art, it is known for an existing automatic transmission to be supplemented by an electric machine in order to permit purely electric or hybrid driving operation of a motor vehicle by the automatic transmission. Normally, a rotor of the electric machine is rotationally fixedly connected to the drive shaft for this purpose. The rotor may however also be connected to a shaft of the automatic transmission which is neither the input nor the output shaft. By way of example, reference is made in this regard to the applicant's publication DE 10 2007 005 438 A1. However, according to the teaching of said publication, the electric machine cannot output or receive power in all gear ratios of said automatic transmission, because said electric machine is arranged on the same shaft as a brake of the automatic transmission.
It is also known for the electric machine to be connected to an existing automatic transmission by a fixed upstream transmission ratio with respect to the drive shaft. By way of example, reference is made in this regard to the applicant's publication DE 10 2008 040 498 A1, wherein a hybrid module with a transmission ratio stage is provided which is connected upstream of the automatic transmission itself. By the fixed upstream transmission ratio, the electric machine is configurable for higher rotational speeds and lower torque, and thus the electric machine has a small structural space requirement. However, the automatic transmission according to the prior art requires an additional planetary gear set for this purpose, and thus the effort for constructing the automatic transmission is increased.